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A274975 Sum of n-th powers of the three roots of x^3-2*x^2-x+1. 3
3, 2, 6, 11, 26, 57, 129, 289, 650, 1460, 3281, 7372, 16565, 37221, 83635, 187926, 422266, 948823, 2131986, 4790529, 10764221, 24186985, 54347662, 122118088, 274396853, 616564132, 1385407029, 3112981337, 6994805571, 15717185450, 35316195134, 79354770147, 178308549978 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(n) is x1^n + x2^n + x3^n, where x1, x2, x3 are the roots of the polynomial x^3-2*x^2-x+1.

x1 = 1/(2*cos(Pi/7)),

x2 = 1/(-2*cos(2*Pi/7)),

x3 = 1/(-2*cos(4*Pi/7)).

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (2,1,-1).

FORMULA

G.f.: -(x^2+4*x-3)/(x^3-x^2-2*x+1). - Alois P. Heinz, Jul 14 2016

a(0)=3, a(1)=2, a(2)=6; thereafter a(n)=2*a(n-1)+a(n-2)-a(n-3).

a(n) = (2*cos(Pi/7))^(-n) + (-2*cos(2*Pi/7))^(-n) + (-2*cos(4*Pi/7))^(-n).

a(n) = A033304(n-1) for n>0.

MATHEMATICA

CoefficientList[Series[-(x^2 + 4 x - 3)/(x^3 - x^2 - 2 x + 1), {x, 0, 32}], x] (* Michael De Vlieger, Jul 14 2016 *)

PROG

(PARI) Vec(-(x^2+4*x-3)/(x^3-x^2-2*x+1) + O(x^50)) \\ Colin Barker, Aug 02 2016

CROSSREFS

Cf. A096975.

3 followed by terms of A033304.

Sequence in context: A109876 A108284 A095011 * A188621 A175182 A052616

Adjacent sequences:  A274972 A274973 A274974 * A274976 A274977 A274978

KEYWORD

nonn,easy

AUTHOR

Kai Wang, Jul 14 2016

STATUS

approved

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Last modified May 25 08:37 EDT 2017. Contains 287015 sequences.